I have a Marantz PM68 integrated amplifier. Some days ago I had to move home. After I reinstalled my audio set, the amp started to sound different to me. Soon I realize that both channels were sounding the same. I moved the balance knob to the right and both channels remain delivering music. I moved the knob to the left and again both channels continues delivering music. In other words the balance knob was not working. Also, when I pushed the source direct button to the "on" position, the system stop sounding. As in my city there is not a Marantz service, I want to have and idea of what is the more probable component is failing, before send it for repair.
It's hard to tell without looking inside the amp. Many modern (read the last ten years) amplifers use a system control IC. It is a large scale chip which controls many of the functions and operations of the entire amp. This would be my first suspicion.